1. Field of Invention
This invention relates to the field of chemical vapor deposition processes for producing films which are useful in magnetic bubble domain devices, and products which may be produced by the process.
2. Prior Art
The current interest in orthoferrite single crystals has been aroused by the ability to produce mobile single wall magnetic or bubble domains in thin plates of proper crystallographic orientation. These domains can be manipulated by magnetic fields to perform logic and memory functions.
Bulk orthoferrite crystals have been grown from solution, either by a molten flux technique, or a hydrothermal technique. Both methods are prone to produce crystals with solvent inclusions or voids. Solvent chemical substitution in the crystal can also occur. Single crystals resulting from either of these growth processes must be sliced and polished down to thin wafers of proper crystallographic orientation. Although very thin orthoferrite layers are desired, the limit of mechanical polishing is a few thousandths of an inch beyond which breakage becomes excessive. In addition, polishing scratches must be eliminated for they impede magnetic domain motion.
Known techniques for obtaining magnetic oxide films on crystalline substrates include spraying a suspension of reactants on heated substrates, vacuum depositing metal alloys with subsequent oxidation, and chemically depositing on a substrate from mixed nitrate solutions followed by firing of the material. More recently, certain films have been prepared by electron beam evaporation and by r-f sputtering.
The use of chemical vapor deposition methods to grow epitaxial layers of specific materials is known in the art. These techniques have been utilized to grow complex metal oxides. In general, chemical vapor deposition methods have produced films with desirable properties but the films have been difficult to reproduce.
There is a minimum domain diameter for each orthoferrite which is characteristic of that material at room temperature and for which a specific sample thickness is required. One way of reducing the characteristic domain diameter that has been described in the literature is to form solid solutions with samarium orthoferrite which has properties that depress the minimum domain diameter.
Sheets or films of polycrystalline magnetizable metals which may be subjected to magnetic influences for the purpose of creating magnetic domains have been shown in U.S. Pat. No. 2,919,432 to K. D. Broadbent. This patent specifically describes a thin sheet domain wall shift register in which a reverse magnetized domain, bounded by leading and trailing domain walls, is nucleated at an input position in the sheet and propagated along a first axis in the sheet by a step-along multiphase propagation field. Such a domain wall device usually requires or is characterized by an anis-tropic magnetic sheet wherein propagation of a reverse domain is either along the easy or the hard axis. The domain walls bounding that reverse domain extend to the edge of the sheet in the direction orthogonal to the axis of propagation. Inasmuch as the walls of the domain are bounded by the edge of the sheet, propagation of the domain is constrained to one of the axes along a transverse direction of the sheet.
In U.S. Pat. No. 3,460,116 to A. H. Bobeck et al.,, it is shown that a reverse magnetized domain may be bounded by a single wall domain. Such a domain differs from the reverse domain propagated in the Broadbent patent in that the single wall domain, encompassing the former, has a cross-sectional shape independent of the breadth of the sheet, or in other words is not bounded by the edge of the sheet. These domains are referred to as single wall domains.
The major disadvantages of both the Broadbent and Bobeck patents are that the former resorts to the use of an anisotropic film or sheet of material which results in striped or finger-like domains substantially across the entire width or length of the sheet, while the latter patent does not utilize a substrate wafer for providing structural support of the sheet of material, thereby preventing the formation of very thin sheets of material for example thicknesses below 25 microns which offer advantages in high domain density applications.